The invention concerns a method of sampling waste gas emissions, especially those containing substances of moderate to low volatility suspended in a gas or aerosol.
The method comprises two steps:
(a) In the first step some of the emissions are withdrawn from the outlet, cooled if necessary, and forwarded to a separator. The substances to be identified, as gases either attached to particles of dust or in a condensate, are subjected to a separation and fixed. PA1 (b) In the second step the substances are extracted and introduced into an analyzer.
Methods of this nature are described in drafts of VDI Guideline 3499, Sheets 1-4: "Messen von polychlorierten Dibenzo(p)dioxinen (PCDD) und Dibenzofuranen (PCDF) in Abgasen industrieller Anlagen und Feuerungsanlagen". This Guideline prescribes how to measure the polychlorinated dibenzo(p)dioxins (PCDD's) and dibenzofurans (PCDF's) in emissions from industrial plants and furnaces.
PCDD's and PCDF's are classes of related chlorinated aromatics. The first comprises 75 and the second 135 homologs. The aforesaid VDI Guideline lists all the isomers and illustrates their structures.
PCDD's and PCDF's derive from the heating or burning of chlorinated organic materials and as undesirable by-products in the manufacture or processing of organochlorine chemicals. They are relatively stable substances that can, however, be broken down in furnaces at high temperatures. The occurrence and chemistry of PCDD's and PCDF's and their toxicologies and ecological hazards have been thoroughly described (cf. the bibliography in the aforecited Guideline).
The Guideline describes standard methods of determining contents of PCDD's and PCDF's. The procedure is intended for the analysis of emissions from a very wide range of sources. Raw, pure, and synthesis gases from internal-combustion engines, domestic furnaces, cement plants, fluidized beds, shredders, landfills, ceramics, metals, and organic- and inorganic-chemicals plants, smelters for specialty recycling, sludge-burning plants, lignite- and anthracite-stoked furnaces, wood-burning plants, oil- and gas-fueled plants, garbage incinerators, and pyrolysis plants are to be analyzed.
The analyzed-gas temperatures can range from -30.degree. to more than 1000.degree. C. The waste gas emissions contain very different levels of water. Dust concentrations can be more than 1 g/m.sup.3, in a raw gas upstream of an electric filter for example.
The procedure described in the VDI Guideline is complicated. The emissions to be analyzed are pumped through a particle filter in the form of a cylinder packed with quartz wool. The filtered gas is forwarded to a condensate separator, where it is cooled to 3.degree. to 20.degree. C. Downstream of the separator is a cartridge packed with a solids adsorbent. Every surface that the sample can come into contact with is glass, with the exception of elbows and part of the filter head, which are titanium. The exhaust pipe can be air-cooled when the emission is hotter than 120.degree. C. The temperatures in the particle filter accordingly range between 80.degree. and 100.degree. C. or even substantially lower.
Every surface that the sample has come into contact with must be washed with recirculating acetone or toluene subsequent to every procedure. The glass liner of the exhaust pipe is generally divided into 10-cm long sections.
The vehicles analyzed are the glass exhaust-pipe liner, the dust-laden quartz wool, the condensate, the solids adsorbent, and the used acetone or toluene rinse.
The result is five subsidiary samples, each of which must be extracted, shaken out, or redissolved. The resulting solutions must then be purified and combined for further processing prior to the actual analysis.
A lot of the moisture in the emissions is removed prior to introduction into the inert filter (sheets 1 & 2), the adsorber (sheets 1, 2 & 4), or the absorber (sheet 3). The moisture is condensed (sheets 2-4) or diluted (sheet 1) out. Dilution entails heating the exhaust pipe to prevent material from condensing onto and possibly adsorbing into its inner surface, leading to erroneous results.
With the known procedure, for due attention to be devoted to all substances of interest, it is necessary to provide either complicated devices that will completely filter the waste gas emissions at low temperatures (sheet 1) or interception of the concentrate somewhere upstream of the last precipitation (adsorption or absorption) to prepare it separately for analysis.
Known apparatus described on sheet 2 of the aforesaid VDI Guideline 3499 essentially comprises a dust filter, a condensate separator, an adsorber, and a suction pump with a flowmeter.
The separator comprises a 2-liter three-neck flask with a cock and two standard-ground joints. Each outer joint accommodates a rapid cooler. The sample flows down through the one cooler (a commercially available high-intensity condenser), through a condensate collector accommodated in a 2-liter mushroom-hooded heater, and through the other cooler (with a radiating area of 3000 cm.sup.2). The droplets precipitate in a downstream glass cylinder packed with Rashig rings. The gas arrives next in a glass cartridge packed with 250 ml of adsorbent resin.
This apparatus is extremely difficult to manage and demands highly trained personnel. Rinsing with and processing the inflammable acetone and toluene and preventing them from escaping into the atmosphere demands extreme caution. The subsequent purification is also very complicated and takes at least an hour.